White, biaxially oriented, flame-retardant and UV-resistant polyester film with cycloolefin copolymer, its use and process for its production

ABSTRACT

The present application relates to a white, biaxially oriented, flame-retardant, UV-resistant polyester film with at least one base layer which comprises, based on the weight of the base layer, from 2 to 60% by weight of a cycloolefin copolymer (COC), where the glass transition temperature of the COC is within the range from 70 to 270° C. The film also comprises from 0.01 to 5.0% by weight of a UV stabilizer as light stabilizer and also comprises from 0.5 to 30% by weight of flame retardant, based in each case on the weight of the layer comprising the UV stabilizer and/or comprising the flame retardant. The film of the invention is suitable for packing foods or other consumable items which are sensitive to light and/or to air, or for use in industry, e.g. in the production of hot-stamping foils or as a label film, or for image-recording papers, printed sheets or magnetic recording cards.

[0001] The present invention relates to a white, biaxially oriented,flame-retardant, UV-resistant polyester film comprising at least onelayer which comprises a polyester and a cycloolefin copolymer (COC). Theinvention further relates to the use of the polyester film, and to aprocess for its production.

BACKGROUND OF THE INVENTION

[0002] White, biaxially oriented polyester films are known from theprior art. These known prior art films are either easy to produce, havegood optical properties or have acceptable processing performance.

[0003] DE-A 2 353 347 describes a process for producing milky polyesterfilm having one or more layers, which comprises preparing a mixture fromparticles of a linear polyester with from 3 to 27% by weight of ahomopolymer or copolymer of ethylene or propylene, extruding the mixtureas a film, quenching the film and biaxially orienting the film viaorientation in directions running perpendicular to one another, andheat-setting the film. A disadvantage of this process is that regrindwhich arises during production of the film (essentially a mixture ofpolyester and ethylene or propylene copolymer) cannot be reused withoutyellowing the film. However, this makes the process uneconomic, but thefilm produced with regrind would not gain acceptance in the market. Inaddition, the roughness of the film is much too high, and this gives thefilm a very matt appearance (very low gloss), undesirable for manyapplications.

[0004] EP-A 0 300 060 describes a single-layer polyester film whichcomprises, besides polyethylene terephthalate, from 3 to 40% by weightof a crystalline propylene polymer and from 0.001 to 3% by weight of asurface-active substance. The effect of the surface-active substance isto increase the number of vacuoles in the film and at the same time toreduce their size to the desired extent. This gives the film greateropacity and lower density. A residual disadvantage of the film is thatregrind which arises during production of the film (essentially amixture of polyester and propylene homopolymer) cannot be reused withoutyellowing the film. However, this makes the film uneconomic, but thefilm produced with regrind would not gain acceptance in the market. Inaddition, the roughness of the film is much too high, giving it a verymatt appearance (very low gloss), undesirable for many applications.

[0005] EP-A 0 360 201 describes a polyester film having at least twolayers and comprising a base layer with fine vacuoles, with a density offrom 0.4 to 1.3 kg/dm3, and having at least one outer layer whosedensity is above 1.3 kg/dm3. The vacuoles are achieved by adding from 4to 30% by weight of a crystalline propylene polymer, followed by biaxialstretching of the film. The additional outer layer improves the ease ofproduction of the film (no streaking on the film surface), and thesurface tension is increased and the roughness of the laminated surfacecan be reduced. A residual disadvantage is that regrind arising duringproduction of the film (essentially a mixture of polyester and propylenehomopolymer) cannot be reused without yellowing the film. However, thismakes the process uneconomic, but the film produced with regrind wouldnot gain acceptance in the market. In addition, the roughnesses of thefilms listed in the examples are still too high, giving the films a mattappearance (low gloss), undesirable for many applications.

[0006] EP-A 0 795 399 describes a polyester film having at least twolayers and comprising a base layer with fine vacuoles, the density ofwhich is from 0.4 to 1.3 kg/dm3, and having at least one outer layer,the density of which is greater than 1.3 kg/dm3. The vacuoles areachieved by adding from 5 to 45% by weight of a thermoplastic polymer tothe polyester in the base, followed by biaxial stretching of the film.The thermoplastic polymers used are, inter alia, polypropylene,polyethylene, polymethylpentene, polystyrene or polycarbonate, and thepreferred thermoplastic polymer is polypropylene. As a result of addingthe outer layer, ease of production of the film is improved (nostreaking on the film surface), the surface tension is increased and theroughness of the laminated surface can be matched to prevailingrequirements. Further modification of the film in the base layer and/orin the outer layers, using white pigments (generally TiO2) and/or usingoptical brighteners permits the properties of the film to be matched tothe prevailing requirements of the application. A residual disadvantageis that regrind which arises during production of the film (essentiallya mixture of polyester and the added polymer) cannot be reused withoutundefined and highly undesirable changes in the color of the film. Thismakes the process uneconomic, but the film produced with regrind wouldnot gain acceptance in the market. In addition, the films listed in theexamples continue to have excessive roughness values, giving them a mattappearance (low gloss), undesirable for many applications.

[0007] DE-A 195 40 277 describes a polyester film having one or morelayers and comprising a base layer with fine vacuoles, with a density offrom 0.6 to 1.3 kg/dm3, and having planar birefringence of from −0.02 to0.04. The vacuoles are achieved by adding from 3 to 40% by weight of athermoplastic resin to the polyester in the base, followed by biaxialstretching of the film. The thermoplastic resins used are, inter alia,polypropylene, polyethylene, polymethylpentene, cyclic olefin polymers,polyacrylic resins, polystyrene or polycarbonate, preferred polymersbeing polypropylene and polystyrene. By maintaining the stated limitsfor the birefringence of the film, the film claimed has in particularsuperior tear strength and superior isotropy properties. However, aresidual disadvantage is that regrind arising during production of thefilm cannot be reused without undefined discoloration of the filmarising, and this in turn is highly undesirable. This makes the processuneconomic, but the film produced with regrind would not gain acceptancein the market. In addition, the roughnesses of the films listed in theexamples are still too high, giving them a matt appearance (low gloss),undesirable for many applications.

[0008] DE-A 23 46 787 describes a flame-retardant polymer. Besides thepolymer itself, its use for producing films and fibers is alsodescribed. However, the following shortcomings were apparent duringproduction of films with this phospholane-modified polymer claimed inthe DE-A:

[0009] The polymer is very sensitive to hydrolysis and has to be verythoroughly predried.

[0010] On drying with dryers of the prior art, the polymer coagulates,making it extremely difficult, or even impossible, to produce a film.

[0011] The films produced, under conditions which are extreme and notcost-effective, embrittle when exposed to heat, i.e. their mechanicalproperties deteriorate sharply due to the rapid onset of embrittlement,making the film industrially unusable. This embrittlement arises afteras little as 48 hours of exposure to heat.

[0012] The object of the present invention was to provide a white,biaxially oriented polyester film which has high gloss and improved easeof production, i.e. low production costs, and which moreover has high UVresistance combined with good heat resistance and flame retardancy. Inparticular, it should be possible for cut material (regrind) directlyassociated with the film production process to be reused in theproduction process at a concentration of from 10 to 70% by weight, basedon the total weight of the film, without any resultant adverse effect onthe physical or optical properties of the film produced with regrind. Inparticular, addition of regrind should not cause any significantyellowing of the film.

[0013] High UV resistance means that the film is damaged only slightlyor not at all by sunlight or other UV radiation, and therefore that thefilms are suitable for outdoor applications and/or critical indoorapplications. In particular, during outdoor use over a period of someyears, the films should not yellow, embrittle or show surface-cracking,nor exhibit any impairment of mechanical properties. High UV resistancetherefore means that the film absorbs UV light and does not begin totransmit light until the visible region has been reached.

[0014] High flame retardancy means that in what is known as a fireprotection test the white film meets the requirements of DIN 4102, Part2 and in particular the requirements of DIN 4102, Part 1 and can beclassified in building materials class B2, in particular B1, forlow-flammability materials.

[0015] The film should moreover pass the UL 94 test known as the“Vertical burning test for flammability of plastic materials”, thereforequalifying for classification 94 VTM-0. This means that the film ceasesto burn within 10 seconds after removal of the bunsen burner, that nofurther smoldering is observed after 30 seconds, and that no flamingdrops are observed over the entire period.

[0016] Cost-effective production includes the capability of the polymersor polymer components needed for producing the flame-retardant film tobe dried using industrial dryers of the prior art. It is important thatthe polymers do not cake and do not undergo thermal degradation. Theseindustrial dryers of the prior art include vacuum dryers, fluidized-beddryers, moving-bed dryers and fixed-bed dryers (power dryers). Thedryers mentioned operate at temperatures of from 100 to 170° C., atwhich flame-retardant polymers usually cake and have to be dug out,making film production impossible.

[0017] In vacuum dryers, which have the gentlest drying action, thepolymer passes through a range of temperature of from about 30 to 130°C. at a pressure of 50 mbar. A process known as postdrying is thenrequired, in a hopper at temperatures of from 100 to 130° C. and with aresidence time of from 3 to 6 hours. Even here, the known polymer cakesto an extreme extent.

[0018] Good heat resistance means that the film and its mechanicalproperties do not deteriorate after 100 hours of annealing at 100° C. ina circulating-air heating cabinet.

DETAILED DESCRIPTION OF THE INVENTION

[0019] According to the invention, the object is achieved by means of awhite, biaxially oriented, flame-retardant and UV-resistant polyesterfilm with at least one base layer made from polyester, thecharacterizing features of which are that at least the base layer alsocomprises, based on the weight of the base layer, from 2 to 60% byweight of a cycloolefin copolymer (COC), where the glass transitiontemperature of the cycloolefin copolymer (COC) is within the range from70 to 270° C., and that the film comprises at least one UV stabilizer aslight stabilizer and a flame retardant, where at least the flameretardant, and preferably also the UV stabilizer, is fed directly as amasterbatch to the polyester during film production.

[0020] The white, biaxially oriented polyester film as defined in thepresent invention is a film of this type whose whiteness is above 70%,preferably above 75% and particularly preferably above 80%. In addition,the opacity of the film of the invention is above 55%, preferably above60% and particularly preferably above 65%.

[0021] To achieve the desired whiteness of the film of the invention,the amount of COC in the base layer should be above 2% by weight,otherwise the whiteness is below 70%. On the other hand, if the amountof COC is above 60% by weight, the film is no longer cost-effective toproduce, since the process of orienting the film becomes unreliable.

[0022] It is also necessary for the glass transition temperature of theCOC used to be above 70° C. Otherwise, if the glass transitiontemperature of the COC used is below 70° C., the polymer mixture isdifficult to process, since it becomes difficult to extrude. The desiredwhiteness is lost and use of regrind gives a film with a tendency towardincreased yellowness. On the other hand, if the glass transitiontemperature of the COC selected is above 270° C. the homogenization ofthe polymer mixture in the extruder will no longer be sufficient. Thisthen gives a film with undesirably inhomogeneous properties.

[0023] In the preferred embodiment of the film of the invention, theglass transition temperature of the COCs used is within the range from90 to 250° C., and in the particularly preferred embodiment it is withinthe range from 110 to 220 C.

[0024] Surprisingly, it has been found that a white, opaque, glossy filmcan be produced by adding a COC in the manner described above.

[0025] The whiteness and the opacity of the film can be adjusted withprecision and adapted to particular requirements by varying the amountand nature of the COC added. This means that the use of other commonlyused whitening or opacifying additives can substantially be dispensedwith. It was also highly surprising that the surface roughness of thefilm is substantially lower, and therefore the gloss of the filmsubstantially higher, than for comparable films of the prior art. Aquite sensational discovery was the additional effect that, despite thepresence of UV stabilizer and flame retardant, regrind exhibits notendency toward yellowing, as is observed when using polymericadditives, sensitive UV stabilizers and conventional flame retardants ofthe prior art.

[0026] None of the features described was foreseeable. This wasparticularly the case since COCs are evidently substantiallyincompatible with polyethylene terephthalate and are known to requirestretching ratios and stretching temperatures similar to those forpolyethylene terephthalate. Under these circumstances the skilled workerwould not have expected that a white, opaque film with high gloss couldbe produced under these production conditions.

[0027] In the preferred and particularly preferred embodiments, the filmof the invention has high/particularly high whiteness andhigh/particularly high opacity, while addition of regrind causesextremely little change in the color of the film.

[0028] The film of the invention comprises at least one UV stabilizer aslight stabilizer, preferably fed by way of what is known as masterbatchtechnology, directly during film production, the amount of UV stabilizerbeing within the range from 0.01 to 5% by weight, based on the weight ofthe layer comprising the UV stabilizer.

[0029] Light, in particular the ultraviolet content of solar radiation,i.e. the wavelength region from 280 to 400 nm, causes degradation inthermoplastics, the results of which are not only a change in appearancedue to color change or yellowing but also an extremely adverse effect onthe mechanical and physical properties of the moldings or films madefrom the thermoplastics.

[0030] The suppression of this photooxidative degradation is ofconsiderable industrial and economic importance, since without it manythermoplastics have drastically reduced scope of application.

[0031] The absorption of UV light by polyethylene terephthalates, forexample, starts below 360 nm, increases markedly below 320 nm and isvery pronounced below 300 nm. Maximum absorption occurs at between 280and 300 nm.

[0032] In the presence of oxygen it is mainly chain cleavage whichoccurs, but without crosslinking. The predominant photooxidationproducts in quantity terms are carbon monoxide, carbon dioxide andcarboxylic acids. Besides the direct photolysis of the ester groups,consideration has to be given to oxidation reactions which proceed viaperoxide radicals, again to form carbon dioxide.

[0033] In the photooxidation of polyethylene terephthalates there canalso be cleavage of hydrogen at the position α to the ester groups,giving hydroperoxides and decomposition products of these, and this maybe accompanied by chain cleavage (H. Day, D. M. Wiles: J. Appl. Polym.Sci 16,1972, p. 203).

[0034] UV stabilizers, i.e. light stabilizers which are UV absorbers,are chemical compounds which can intervene in the physical and chemicalprocesses of light-induced degradation. Carbon black and other pigmentscan give some protection from light. However, these substances areunsuitable for pale-coloured films, since they cause discoloration orcolor change.

[0035] For the purposes of the invention, light stabilizers which aresuitable UV stabilizers are those which absorb at least 70%, preferably80%, particularly preferably 90%, of the UV light in the wavelengthregion from 180 to 380 nm, preferably from 280 to 350 nm. These areparticularly suitable if they are thermally stable, i.e. do notdecompose into cleavage products, or cause evolution of gas, in thetemperature range from 260 to 300° C. Examples of light stabilizerswhich are suitable UV stabilizers are 2-hydroxybenzophenones,2-hydroxybenzotriazoles, organonickel compounds, salicylic esters,cinnamic ester derivatives, resorcinol monobenzoates, oxanilides,hydroxybenzoic esters, sterically hindered amines and triazines,preferably the 2-hydroxybenzotriazoles and the triazines.

[0036] For the skilled worker it was highly surprising that the use ofthe combination according to the invention, made from COC and UVstabilizers with flame retardant, gave useful films with excellentproperties. The person skilled in the art would probably have begun byattempting to achieve some degree of UV resistance by using anantioxidant, but would have immediately found that the film rapidlyyellows on weathering.

[0037] With the background knowledge that UV stabilizers which absorb UVlight and therefore have the potential for protection are known from theliterature, the skilled worker would then probably have usedcommercially available UV stabilizers. He would then have found that

[0038] the UV stabilizer has insufficient thermal stability anddecomposes into cleavage products at temperatures of from 200 to 240°C., or causes evolution of gas, and

[0039] he has to incorporate large amounts (from about 10 to 15% byweight) of UV stabilizer if the UV light is to be absorbed effectively,thus preventing damage to the film.

[0040] However, at these high concentrations he would have found thatthe film is yellow even immediately after production, with YellownessIndex differences (YID) around 25. He would also have found thatmechanical properties are adversely affected. During orientation hewould have encountered exceptional problems, such as:

[0041] break-off due to lack of strength, i.e. modulus of elasticity;

[0042] die deposits, causing variations in profile;

[0043] roller deposits from the UV stabilizer, an effect causingimpairment of optical properties (poor haze, adhesion problems,non-uniform surface);

[0044] deposits in the stretching and setting frames, dropping onto thefilm.

[0045] It was therefore more than surprising that even lowconcentrations of the UV stabilizer of the invention achieve excellentUV protection. It was very surprising that, together with this excellentUV protection,

[0046] the Yellowness Index of the film is unchanged from that of anunstabilized film within the bounds of accuracy of measurement;

[0047] there are no releases of gases, no die deposits and no framecondensation, and the film therefore has excellent optical propertiesand excellent profile and layflat;

[0048] the UV-resistant film has excellent stretchability, and thereforecan be produced in a reliable and stable manner on high-speed film linesat speeds of up to 420 m/min.

[0049] The film is therefore also cost-effective. It was also highlysurprising that it is even possible to reuse regrind without any adverseeffect on the Yellowness Index of the film.

[0050] If desired, the film of the invention may also comprise, based onthe weight of the polyester, from 0 to 50 000 ppm, in particular from 20to 30 000 ppm, particularly preferably from 50 to 25 000 ppm, of anoptical brightener. The optical brightener is preferably fed to thepolyester by way of what is known as masterbatch technology during filmproduction.

[0051] The optical brighteners which may, if desired, be added arecapable of absorbing UV radiation in the region from 360 to 380 nm andre-emitting this as longer-wavelength, visible blue-violet light.

[0052] Suitable optical brighteners are bisbenzoxazoles, phenylcoumarinsand bisstearylbiphenyls, in particular phenylcoumarin, and particularpreference is given to triazine phenylcoumarin, obtainable as ®Tinopalfrom Ciba-Geigy, Basle, Switzerland and ®Hostalux KS (Clariant,Germany), and also ®Eastobrite OB-1 (Eastman).

[0053] Besides the optical brightener, soluble blue dyes may also beadded to the polyester if appropriate. Blue dyes which have provensuitable are cobalt blue, ultramarine blue and anthraquinone dyes, inparticular®Sudan Blue 2 (BASF, Ludwigshafen, Germany).

[0054] The amounts used of the blue dyes are from 0 to 10 000 ppm, inparticular from 20 to 5000 ppm, particularly preferably from 50 to 1000ppm, based on the weight of the polyester.

[0055] In one particularly preferred embodiment, the film of theinvention comprises from 0.1 to 5.0% by weight of 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-hexyloxyphenol of the formula:

[0056] or from 0.1to 5.0% by weight of2,2′-methylenebis(6-(2H-benzotriazol-2-yl)-4-(1,1,2,2-tetramethylpropyl)phenol) of the formula

[0057] In another embodiment it is also possible to use mixtures ofthese two UV stabilizers or mixtures of at least one of these two UVstabilizers with other UV stabilizers, the total concentration of lightstabilizers preferably being from 0.1 to 5.0% by weight, preferablywithin the range from 0.5 to 3.0% by weight, based on the weight of thebase layer.

[0058] The film of the invention comprises at least one flame retardant,which is fed by way of what is known as masterbatch technology directlyduring film production, the concentration of the flame retardant beingwithin the range from 0.5 to 30.0% by weight, preferably from 1.0 to20.0% by weight, based on the weight of the layer which comprises theflame retardant. During production of the masterbatch, the relationshipbetween flame retardant and thermoplastic is generally within the rangefrom 60% by weight: 40% by weight to 10% by weight: 90% by weight.

[0059] Typical flame retardants include bromine compounds,chloroparaffins and other chlorine compounds, antimony trioxide, andalumina trihydrates, the halogen compounds being disadvantageous sincethey produce halogen-containing byproducts. Other serious disadvantagesare the low lightfastness of films in which these compounds are present,and the evolution of hydrogen halides in the event of a fire.

[0060] Examples of suitable flame retardants used according to theinvention are organic phosphorus compounds, such as carboxyphosphinicacids, anhydrides thereof and dimethyl methylphosphonate. It isimportant for the invention that the organic phosphorus compound issoluble in the thermoplastic, since otherwise the optical propertiesrequired are not complied with.

[0061] Since the flame retardants generally have some degree ofsusceptibility to hydrolysis, concomitant use of a hydrolysis stabilizermay be advisable.

[0062] The hydrolysis stabilizers used are generally amounts of from0.01 to 1.0% by weight of phenolic stabilizers, of alkali metal/alkalineearth metal stearates and/or of alkali metal/alkaline earth metalcarbonates. The amounts of phenolic stabilizers used are preferably from0.05 to 0.6% by weight, in particular from 0.15 to 0.3% by weight, andtheir molar mass is preferably above 500 g/mol. Particularlyadvantageous compounds are pentaerythrityltetrakis-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene.

[0063] It was more than surprising that by using masterbatch technologyand a suitable predrying and/or precrystallization procedure and, ifdesired, using small amounts of a hydrolysis stabilizer, it is possibleto produce a flame-retardant, thermoformable film with the requiredproperty profile cost-effectively and especially without any caking inthe dryer, and that on exposure to high temperature the film does notembrittle, and does not break when folded.

[0064] It was very surprising that, together with this excellent resultand with the flame retardancy required, and with the high UV resistance:

[0065] the Yellowness Index of the film undergoes no adverse change whencompared with that of an unstabilized film, within the bounds ofaccuracy of measurement;

[0066] there are no releases of gases, no die deposits and no framecondensation, and the film therefore has excellent optical propertiesand excellent profile and layflat;

[0067] the flame retardant, UV-resistant film has excellentstretchability, and therefore can be produced in a reliable and stablemanner on high-speed film lines at speeds of 420 m/min.

[0068] The film is therefore also cost-effective.

[0069] The film of the invention has one or more layers. Single-layerembodiments have a structure like that of the COC-containing layerdescribed below. Embodiments having more than one layer have at leasttwo layers and always comprise the COC-containing layer and at least oneother layer, where the COC-containing layer is the base layer but mayalso form the intermediate layer or the outer layer of the film havingtwo or more layers. In one preferred embodiment, the COC-containinglayer forms the base layer of the film with at least one outer layer andpreferably outer layers on both sides, and an intermediate layer orintermediate layers may be present, if desired, on one or both sides. Inanother preferred embodiment, the COC-containing layer also forms anintermediate layer of the multilayer film. Other embodiments withCOC-containing intermediate layers have a five-layer structure withCOC-containing intermediate layers on both sides of the COC-containingbase layer. In another embodiment, the COC-containing layer may form, aswell as the base layer, an outer layer or outer layers on the base layeror intermediate layer, on one or both sides. For the purposes of thepresent invention, the base layer is that layer which makes up more thanfrom 50 to 100%, preferably from 70 to 90%, of the total film thickness.The outer layer is always the layer which forms the outer layer of thefilm, and it is preferable for the invention if one or two outer layershave been arranged on the COC-containing base layer, and if both the UVstabilizer and the flame retardant are present in the outer layer(s).

[0070] Each embodiment of the invention is a non-transparent, whitefilm. For the purposes of the present invention, non-transparent filmsare those films whose light transmittance to ASTM D1 003-77 is below95%, preferably below 75%.

[0071] The COC-containing layer (the base layer) of the film of theinvention comprises a polyester, preferably a polyester homopolymer, aCOC, the UV stabilizer, the flame retardant, and also, if desired, otheradditives, in each case in effective amounts. This layer generallycomprises at least 20% by weight, preferably from 40 to 96% by weight,in particular from 70 to 96% by weight, of polyester, based on theweight of the layer.

[0072] The base layer of the film comprises, as main constituent, athermoplastic polyester. Polyesters suitable here are those made fromethylene glycol and terephthalic acid (=polyethylene terephthalate,PET), from ethylene glycol and naphthalene-2,6-dicarboxylic acid(=polyethylene 2,6-naphthalate, PEN), from1,4-bishydroxymethylcyclohexane and terephthalic acid(=poly-1,4-cyclohexanedimethylene terephthalate, PCDT) or else fromethylene glycol, naphthalene-2,6-dicarboxylic acid andbiphenyl-4,4′-dicarboxylic acid (=polyethylene 2,6-naphthalatebibenzoate, PENBB). Particular preference is given to polyesters whichare composed of at least 90 mol %, preferably at least 95 mol %, ofethylene glycol units and terephthalic acid units or ethylene glycolunits and naphthalene-2,6-dicarboxylic acid units. The remaining monomerunits are derived from other aliphatic, cycloaliphatic or aromatic diolsand, respectively, dicarboxylic acids, as may also be present in layer A(A=outer layer 1) or in layer C (C=outer layer 2) of a multilayered ABC(B=base layer) film.

[0073] Examples of other suitable aliphatic diols are diethylene glycol,triethylene glycol, aliphatic glycols of the formula HO—(CH2)n—OH, wheren is an integer from 3 to 6 (in particular 1,3-propanediol,1,4-butanediol, 1,5-pentanediol and 1,6-hexanediol) or branchedaliphatic glycols having up to 6 carbon atoms. Among the cycloaliphaticdiols, mention should be made of cyclohexanediols (in particular 1,4-cyclohexanediol). Other suitable aromatic diols are those, forexample, of the formula HO—C6H4-X-C6H4—OH where X is —CH2—, —C(CH3)2—,—C(CF3)2—, —O—, —S— or —SO2—. Bisphenols of the formula HO—C6H4—C6H4—OHare also highly suitable.

[0074] Other preferred aromatic dicarboxylic acids arebenzenedicarboxylic acids, naphthalenedicarboxylic acids (such asnaphthalene-1,4- or -1,6-dicarboxylic acid), biphenyl-x,x′-dicarboxylicacids (in particular biphenyl-4,4′-dicarboxylic acid),diphenylacetylene-x,x′-dicarboxylic acids (in particulardiphenylacetylene-4,4′-dicarboxylic acid) and stilbene-x,x′-dicarboxylicacids. Among the cycloaliphatic dicarboxylic acids mention should bemade of cyclohexanedicarboxylic acids (in particularcyclohexane-1,4-dicarboxylic acid). Among the aliphatic dicarboxylicacids, the (C3-C19)-alkanedioic acids are particularly suitable, wherethe alkane moiety may be straight-chain or branched.

[0075] The polyesters may, for example, be prepared by thetransesterification process. The starting materials here aredicarboxylic esters and diols, and these are reacted using the usualtransesterification catalysts, such as salts of zinc, of calcium, oflithium, of magnesium or of manganese. The intermediates are thenpolycondensed in the presence of typical polycondensation catalysts,such as antimony trioxide or titanium salts. They may equally well beprepared by the direct esterification process in the presence ofpolycondensation catalysts, starting directly from the dicarboxylicacids and the diols.

[0076] According to the invention, the COC-containing layer (base layer)or, in the case of single-layer embodiments, the film, comprises anamount of not less than 2.0% by weight, preferably from 4 to 50% byweight and particularly preferably from 6 to 40% by weight, of acycloolefin copolymer (COC), based on the weight of the base layer or,in the case of single-layer embodiments, based on the weight of thefilm. It is significant for the present invention that the COC is notcompatible with the polyethylene terephthalate and does not form ahomogeneous mixture with the same.

[0077] Cycloolefin polymers are homopolymers or copolymers which containpolymerized cycloolefin units and, if desired, acyclic olefins ascomonomer. Cycloolefin polymers suitable for the present inventioncontain from 0.1 to 100% by weight, preferably from 10 to 99% by weight,particularly preferably from 50 to 95% by weight, of polymerizedcycloolefin units, in each case based on the total weight of thecycloolefin polymer. Particular preference is given to polymers whichhave been built up using the monomers comprising the cyclic olefins ofthe formulae I, II, III, IV, V or VI:

[0078] R1, R2, R3, R4, R5, R6, R7 and R8 in these formulae are identicalor different and are a hydrogen atom or a C1-C30-hydrocarbon radical, ortwo or more of the radicals R1 to R8 have been bonded cyclically, andthe same radicals in the different formulae may have the same or adifferent meaning. Examples of C1-C30-hydrocarbon radicals are linear orbranched C1-C8-alkyl radicals, C6-C18-aryl radicals, C7-C20-alkylenearylradicals and cyclic C3-C20-alkyl radicals and acyclic C2-C20-alkenylradicals.

[0079] If desired, the COCs may contain from 0 to 45% by weight, basedon the total weight of the cycloolefin polymer, of polymerized units ofat least one monocyclic olefin of the formula VII:

[0080] n here is a number from 2 to 10.

[0081] If desired, the COCs may contain from 0 to 99% by weight, basedon the total weight of the COC, of polymerized units of an acyclicolefin of the formula VIII:

[0082] R9, R10, R11 and R12 here are identical or different and are ahydrogen atom or a C1-C10-hydrocarbon radical, e.g. a C1-C8-alkylradical or a C6-C14-aryl radical.

[0083] Other polymers suitable in principle are cycloolefin polymerswhich are obtained by ring-opening polymerization of at least one of themonomers of the formulae I to VI, followed by hydrogenation.

[0084] Cycloolefin homopolymers have a structure composed of one monomerof the formulae I to VI. These cycloolefin polymers are less suitablefor the purposes of the present invention. Polymers suitable for thepurposes of the present invention are cycloolefin copolymers (COC) whichcomprise at least one cycloolefin of the formulae I to VI and acyclicolefins of the formula VII as comonomer. Acyclic olefins preferred hereare those which have from 2 to 20 carbon atoms, in particular unbranchedacyclic olefins having from 2 to 10 carbon atoms, for example ethylene,propylene and/or butylene. The proportion of polymerized units ofacyclic olefins of the formula VIII is up to 99% by weight, preferablyfrom 5 to 80% by weight, particularly preferably from 10 to 60% byweight, based on the total weight of the respective COC.

[0085] Among the COCs described above, those which are particularlypreferred contain polymerized units of polycyclic olefins having afundamental nor-bornene structure, particularly preferably norbornene ortetracyclododecene. Particular preference is also given to COCs whichcontain polymerized, units of acyclic olefins, in particular ethylene.Particular preference is in turn given to norbomene-ethylene copolymersand tetracyclododecene-ethylene copolymers which in each case containfrom 5 to 80% by weight, preferably from 10 to 60% by weight, ofethylene (based on the weight of the copolymer).

[0086] The cycloolefin polymers generically described above generallyhave glass transition temperatures Tg in the range from −20 to 400° C.However, COCs which can be used for the invention have a glasstransition temperature Tg above 70° C., preferably above 90° C. and inparticular above 110° C. The viscosity number (decalin, 135° C., DIN 53728) is advantageously from 0.1 to 200 ml/g, preferably from 50 to 150ml/g.

[0087] The COCs are prepared by heterogeneous or homogeneous catalysiswith organometallic compounds, as described in a wide variety ofdocuments. Suitable catalyst systems based on mixed catalysts made fromtitanium compounds and, respectively, vanadium compounds in conjunctionwith aluminum organyl compounds are described in DD 109 224, DD 237 070and EP-A-0 156 464. EP-A-0 283 164, EP-A-0 407 870, EP-A-0 485 893 andEP-A-0 503 422 describe the preparation of COCs with catalysts based onsoluble metallocene complexes. The preparation processes for COCsdescribed in the abovementioned specifications are expresslyincorporated herein by way of reference.

[0088] The COCs are incorporated into the film either in the form ofpure granules or in the form of granulated concentrate (masterbatch), bypremixing the polyester granules or polyester powder with the COC or,respectively, with the COC masterbatch, followed by feeding to anextruder. In the extruder, the mixing of the components continues andthey are heated to the processing temperature. It is advantageous herefor the novel process if the extrusion temperature is above the glasstransition temperature Tg of the COC, generally above the glasstransition temperature of the COC by at least 5 K, preferably by from 10to 180 K, in particular by from 15 to 150 K.

[0089] For the intermediate layers and for the outer layers, it ispossible in principle to use the polymers used for the base layer.Besides these, other materials may also be present in the outer layers,and the outer layers are then preferably composed of a mixture ofpolymers or of a copolymer or of a homopolymer which comprise ethylene2,6-naphthalate units and ethylene terephthalate units. Up to 30 mol %of the polymers may be composed of other comonomers (e.g. ethyleneisophthalate units).

[0090] The base layer and the other layers may additionally compriseconventional additives, such as stabilizers, antiblocking agents andother fillers. They are advantageously added to the polymer or,respectively, to the polymer mixture prior to melting. Examples ofstabilizers used are phosphorus compounds, such as phosphoric acid orphosphoric esters.

[0091] Typical antiblocking agents (in this context also termedpigments) are inorganic and/or organic particles, such as calciumcarbonate, amorphous silica, talc, magnesium carbonate, bariumcarbonate, calcium sulfate, barium sulfate, lithium phosphate, calciumphosphate, magnesium phosphate, aluminum oxide, lithium fluoride, thecalcium, barium, zinc or manganese salts of the dicarboxylic acids used,carbon black, titanium dioxide, kaolin or crosslinked polymer particles,e.g. polystyrene particles or acrylate particles.

[0092] The additives selected may also comprise mixtures of two or moredifferent antiblocking agents or mixtures of antiblocking agents of thesame composition but different particle sizes. The particles may beadded to the polymers of the individual layers of the film in therespective advantageous amounts, e.g. as a glycolic dispersion duringthe polycondensation or via masterbatches during extrusion. Pigmentconcentrations which have proven particularly suitable are from 0 to 25%by weight (based on the weight of the respective layer). EP-A-0 602 964,for example, describes the antiblocking agents in detail.

[0093] To improve the whiteness of the film, the base layer or the otheradditional layers may comprise further pigmentation. It has provenparticularly advantageous here for the additional materials added to bebarium sulfate with a particle size of from 0.3 to 0.8 μm, preferablyfrom 0.4 to 0.7 μm, or titanium dioxide with a particle size of from0.05 to 0.3 μm. This gives the film a brilliant white appearance. Theconcentration of barium sulfate or titanium dioxide is within the rangefrom 1 to 25% by weight, preferably from 1 to 20% by weight, and verypreferably from 1 to 15% by weight.

[0094] The total thickness of the film may vary within wide limits anddepends on the application envisaged. The preferred embodiments of thenovel film have total thicknesses of from 4 to 400 μm, preferably from 8to 300 μm, particularly preferably from 10 to 300 μm. The thickness ofany intermediate layer(s) present is/are, in each case independently ofone another, from 0.5 to 15 μm, preferably from 1 to 10 μm, inparticular from 1 to 8 μm. All the values given are based on oneintermediate layer. The thickness of the outer layer(s) is selectedindependently of the other layers and is preferably within the rangefrom 0.1 to 10 μm, in particular from 0.2 to 5 μm, preferably from 0.3to 2 μm, and outer layers applied on both sides may be identical ordifferent in terms of their thickness and composition. The thickness ofthe base layer is therefore given by the difference between the totalthickness of the film and the thickness of the outer and intermediatelayer(s) applied, and, similarly to the total thickness, may thereforevary within wide limits.

[0095] In one particular embodiment, the outer layers may also becomposed of a polyethylene naphthalate homopolymer, or of an ethyleneterephthalate-ethylene naphthalate copolymer, or of a compound.

[0096] In this embodiment, the standard viscosity of the thermoplasticsof the outer layers is similar to that of the polyethylene terephthalateof the base layer.

[0097] In the embodiment having two or more layers, the UV stabilizer ispreferably present in the outer layers. If required, the base layer mayalso have a UV stabilizer.

[0098] In the embodiments having two or more layers, the flame retardantis preferably present in the base layer. However, the outer layers may,if required, also have flame retardant.

[0099] In another embodiment, flame retardant and UV stabilizer may bepresent in the outer layers. If required, or if fire-protectionrequirements are stringent, the base layer may additionally comprisewhat is known as a base level of flame retardant.

[0100] Unlike in the single-layer embodiment, the amount of flameretardant and UV stabilizer here in percent by weight is based on theweight of the respective layer having the agents.

[0101] Very surprisingly, weathering tests to the ISO 4892 testspecification using the Atlas Ci65 Weather-Ometer show that, to achieveimproved UV resistance in a three-layer film, it is fully sufficient forthe outer layers of from 0.5 to 2 μm thickness to have UV stabilizers.

[0102] It is also surprising that fire tests to DIN 4102 Part 1 and Part2, and also the UL 94 test, have shown that films of the inventioncomply with the requirements.

[0103] The flame-retardant, UV-resistant films having two or more layersand produced by known coextrusion technology are therefore of greatinterest in economic terms when compared with monofilms provided withfull UV-resistance and flame retardancy, since markedly less additivesare needed to achieve comparable flame retardancy and UV resistance.

[0104] Results from weathering tests reveal that the flame-retardant,white, UV-resistant films of the invention generally show no increase inyellowing, no embrittlement, no loss of surface gloss, nosurface-cracking and no impairment of mechanical properties even afterfrom 5 to 7 years (extrapolated from the individual weathering testscarried out) of outdoor use.

[0105] During production of the film it was found that theflame-retardant, UV-resistant film gives excellent longitudinal andtransverse orientation without break-offs. In addition, no gas releasesof any type attributable to the presence of UV stabilizer or flameretardant were found, and this is important for the invention, sincemost conventional UV stabilizers and flame retardants evolve veryundesirable and unpleasant gases, attributable to the decomposition ofthese compounds under the conditions of processing, at extrusiontemperatures above 260° C., and are therefore of no use.

[0106] Surprisingly, even films of the invention in the range ofthickness from 5 to 300 μm comply with requirements for the constructionmaterials class B1 to DIN 4102 Part 1 and with those for the UL 94 test.

[0107] During production of the white, flame-retardant, UV-resistantfilm it was also found that the flame retardant can be incorporatedusing masterbatch technology and suitable predrying and/orprecrystallization of the flame retardant masterbatch without theoccurrence of caking in the dryer, and therefore the film can beproduced cost-effectively.

[0108] It was more than surprising that incorporation is made eveneasier by small additions of a hydrolysis stabilizer within the flameretardant masterbatch. Throughputs, and therefore production rates,could readily be increased in this way. In one very specific embodiment,the film also comprises small amounts of a hydrolysis stabilizer in thelayers having flame retardant.

[0109] Measurements showed that the film of the invention does notembrittle over long periods at high temperatures of 100° C., a factwhich is more than surprising. This result is attributable to thesynergistic action of suitable precrystallization, predrying,masterbatch technology and provision of UV stabilizer.

[0110] The film of the invention can moreover readily be recycledwithout pollution of the environment and without loss of mechanicalproperties, and examples of uses for which it is suitable are thereforeshort-lived promotional placards for constructing exhibition stands andother promotional requisites where fire protection is desirable.

[0111] The invention further provides a process for producing thepolyester film of the invention by the extrusion or coextrusion processknown per se.

[0112] According to the invention, the flame retardant, with or withoutthe hydrolysis stabilizer, is fed by way of masterbatch technology. Theflame retardant is fully dispersed in a carrier material. Carriermaterials which may be used are the polyester itself, e.g. thepolyethylene terephthalate, or else other polymers compatible with thepolyester.

[0113] According to the invention, the UV stabilizer may be added at anearly stage by the producer of the polyester, or may be fed into theextruder during film production.

[0114] It is particularly preferable for the UV stabilizer to be addedby way of masterbatch technology. The UV stabilizer is fully dispersedin a solid carrier material. Carrier materials which may be used arecertain resins, the polyester itself, e.g. the polyethyleneterephthalate, or else other polymers compatible with the polyester.

[0115] It is important in masterbatch technology that the particle sizeand the bulk density of the masterbatch are similar to the particle sizeand the bulk density of the polyester, so that homogeneous distributionis achieved, giving uniform UV stabilization.

[0116] The polyester films may be produced by known processes frompolyester with, if desired, other polymers, with the flame retardant,with or without the hydrolysis stabilizer, with the UV stabilizer and/orwith other customary additives in customary amounts of from 1.0 to amaximum of 30% by weight, either in the form of a monofilm or else inthe form of, if desired coextruded, films having two or more layers andwith identically or differently constructed surfaces, where one surfacemay have been pigmented, for example, but no pigment is present at theother surface. Known processes may also have been used to provide one orboth surfaces of the film with a conventional functional coating.

[0117] It is important for the invention that the masterbatch whichcomprises the flame retardant and, if used, the hydrolysis stabilizer,is precrystallized or predried. This predrying includes, for example,gradual heating of the masterbatch at reduced pressure (from 20 to 80mbar, preferably from 30 to 60 mbar, in particular from 40 to 50 mbar)with agitation, and, if desired, post-drying at a constant, elevatedtemperature, again at reduced pressure. It is preferable for themasterbatch to be charged at room temperature from a metering vessel inthe desired blend together with the polymer of the base and/or outerlayers and, if desired, with other raw material components batchwiseinto a vacuum dryer in which the temperature profile moves from 10 to160° C., preferably from 20 to 150° C., in particular from 30 to 130°C., during the course of the drying time or residence time. During theresidence time of about 6 hours, preferably 5 hours, in particular 4hours, the raw material mixture is stirred at from 10 to 70 rpm,preferably from 15 to 65 rpm, in particular from 20 to 60 rpm. Theresultant precrystallized or predried raw material mixture is post-driedin a downstream vessel, likewise evacuated, at temperatures of from 90to 180° C., preferably from 100 to 170° C., in particular from 110 to160° C., for from 2 to 8 hours, preferably from 3 to 7 hours, inparticular from 4 to 6 hours.

[0118] For the coextrusion process, the procedure is that the melt(s)corresponding to the single-layer film or to the individual layers ofthe film is/are extruded/coextruded through a flat-film die, theresultant film is drawn off for solidification on one or more rolls, thefilm is then biaxially stretched (oriented), and the biaxially stretchedfilm is then heat-set and, if desired, corona- or flame-treated on thesurface layer intended for further treatment.

[0119] The biaxial orientation is generally carried out in succession.For this, it is preferable to orient first longitudinally (i.e. in MD,the machine direction) and then transversely (i.e. in TD,perpendicularly to the machine direction). This orientates the molecularchains. The longitudinal orientation preferably takes place with the aidof two rolls rotating at different rates corresponding to the desiredstretching ratio. For the transverse stretching, an appropriate suitabletenter frame is generally used.

[0120] Simultaneous orientation of the film of the invention in the twodirections (MD and TD) with the aid of a tenter frame suitable for thispurpose has proven not to be appropriate, since this stretching methodgives a film which has insufficient whiteness and insufficient opacity.

[0121] The temperature at which the orientation is carried out may bevaried over a relatively wide range and depends on the propertiesdesired in the film. In general, the longitudinal stretching is carriedout at from 80 to 130° C. and the transverse stretching at from 90 to150° C. The longitudinal stretching ratio is generally within the rangefrom 2.5:1 to 6:1, preferably from 3:1 to 5.5:1. The transversestretching ratio is generally within the range from 3.0:1 to 5.0:1,preferably from 3.5:1 to 4.5:1.

[0122] In the heat-setting which follows, the film is held at atemperature of from 150 to 250° C. for from about 0.1 to 10 s. The filmis then cooled and then wound up in the usual manner.

[0123] To establish other desired properties, the film may be chemicallytreated or else corona- or, respectively, flame-treated. The intensityof treatment is selected such that the surface tension of the film isgenerally above 45 mN/m.

[0124] To establish other properties, the film may also be coated.Typical coatings have adhesion-promoting, antistatic, slip-improving orrelease action. It is clear that these additional coatings may beapplied to the film by in-line coating using aqueous dispersions, priorto the transverse stretching procedure.

[0125] The particular advantage of the novel film is its high whitenessand high opacity, together with UV resistance and flame retardancy.Surprisingly, the gloss of the film was also very high. The whiteness ofthe film is above 70%, preferably above 75% and particularly preferablyabove 80%. The opacity of the novel film is above 55%, preferably above60% and particularly preferably above 65%. The gloss of the novel filmis above 80, preferably above 90 and particularly preferably above 100.

[0126] Another particular advantage of the invention is that regrindmaterial produced directly during the production process can be reusedat a concentration of from 10 to 70% by weight, based on the totalweight of the film, without any significant negative effect on thephysical properties of the film. In particular, the regrinded material(composed essentially of polyester and COC) does not give undefinedchanges in the color of the film, as is the case in the films of theprior art.

[0127] A further advantage of the invention is that the production costsof the novel film are comparable with those of conventional opaque filmsof the prior art. The other properties of the novel film relevant to itsprocessing and use remain essentially unchanged or are even improved.

[0128] The film has excellent suitability for packing foods or otherconsumable items which are sensitive to light and/or to air. It is alsohighly suitable for use in the industrial sector, e.g. for producinghot-stamping foils or as a label film. Besides this, the film is, ofcourse, particularly suitable for image-recording papers, printedsheets, magnetic recording cards, to name just a few possibleapplications.

[0129] The processing performance and winding performance of the film,in particular on high-speed machines (winders, metallizers, printingmachines and laminating machines) is exceptionally good. A measure ofprocessing performance is the coefficient of friction of the film, whichis below 0.6. A decisive factor affecting winding performance, besides agood thickness profile, excellent layflat and a low coefficient offriction, is the roughness of the film. It has become apparent that thewinding of the novel film is particularly good if the average roughnessis within the range from 50 to 250 nm while the other properties arecomplied with. The roughness may be varied within the stated range by,inter alia, varying the COC concentration and the process parameters inthe production process.

[0130] The most important film properties according to the invention areagain summarized at a glance in the table below (Table 1), thusproviding a particularly clear picture.

[0131] The following values were measured to characterize the polymersand the films:

[0132] SV (DCA), IV (DCA)

[0133] The standard viscosity SV (DCA) is measured in dichloroaceticacid by analogy with DIN 53726.

[0134] The intrinsic viscosity (IV) is calculated as follows from thestandard viscosity (SV)

IV (DCA)=6.67·10−4 SV (DCA)+0.118

[0135] Surface defects and uniformity of coloration

[0136] Surface defects and uniformity of coloration are determinedvisually.

[0137] Weathering (on both sides) and UV resistance

[0138] UV resistance is tested as follows to the ISO 4892 testspecification: Test equipment Atlas Ci65 Weather-Ometer Test conditionsISO 4892, i.e. artificial weathering Irradiation time 1000 hours (perside) Irradiation 0.5 W/m2, 340 nm Temperature 63° C. Relative humidity50% Xenon lamp Internal and external filter made from borosilicateIrradiation cycles 102 minutes of UV light, then 18 minutes of UV lightwith water spray on the specimens, then again 102 minutes of UV light,etc.

[0139] Yellowness Index

[0140] The Yellowness Index YID is the deviation from the colorlessstate in the “yellow” direction and is measured to DIN 6167.

[0141] Fire performance

[0142] Fire performance is determined to DIN 4102, Part 2, constructionmaterials class B2, and to DIN 4102, Part 1, construction materialsclass B1, and also by the UL 94 test.

[0143] Coefficient of friction

[0144] Coefficient of friction is determined to DIN 53 375. Thecoefficient of sliding friction was determined 14 days after production.

[0145] Surface tension

[0146] Surface tension was determined by what is known as the ink method(DIN 53 364).

[0147] Roughness

[0148] Roughness Ra of the film was determined to DIN 4768 with acut-off of 0.25 mm.

[0149] Whiteness and opacity

[0150] Whiteness and opacity were determined with the aid of a Zeiss,Oberkochem (DE) “ELREPHO” electric reflectance photometer, standardilluminant C, 2° normal observer. Opacity is determined to DIN 53 146.Whiteness is defined as W=RY+3RZ−3RX.

[0151] W=whiteness, RY, RZ and RX=relevant reflection factors when theY, Z and X color-measurement filter is used. The white standard used wasa barium sulfate pressing (DIN 5033, Part 9). A detailed description isgiven, for example, in Hansl Loos “Farbmessung” [Color measurement],Verlag Beruf und Schule, Itzehoe (1989).

[0152] Light transmittance

[0153] Light transmittance is measured using a method based on ASTMD1033-77.

[0154] Gloss

[0155] Gloss was determined to DIN 67 530. The reflectance was measuredas an optical value characteristic of a film surface. Based on thestandards ASTM-D 523-78 and ISO 2813, the angle of incidence was set at60°. A beam of light hits the flat test surface at the set angle ofincidence and is reflected and/or scattered by this surface. Aproportional electrical variable is displayed representing light beamshitting the photoelectronic detector. The value measured isdimensionless and must be stated together with the angle of incidence.

[0156] Glass transition temperature

[0157] The glass transition temperature Tg was determined using filmspecimens with the aid of DSC (differential scanning calorimetry) (DIN73 765). A DuPont DSC 1090 was used. The heating rate was 20 K/min andthe specimen weight was about 12 mg. The glass transition Tg wasdetermined in the first heating procedure. Many of the specimens showedan enthalpy relaxation (a peak) at the beginning of the step-like glasstransition. The temperature taken as Tg was that at which the step-likechange in heat capacity—without reference to the peak-shaped enthalpyrelaxation—achieved half of its height in the first heating procedure.In all cases, there was only a single glass transition observed in thethermogram in the first heating procedure.

EXAMPLE 1

[0158] Chips of polyethylene terephthalate (prepared by thetransesterification process using Mn as transesterification catalyst, Mnconcentration: 100 ppm) were dried at 150° C. to a residual moisturebelow 100 ppm and fed to the extruder for the base layer B. Alongsidethis, chips of ®Topas 6015 cycloolefin copolymer (COC) from Ticona (COCcomposed of 2-norbornene and ethylene, see also W. Hatke: Folien aus COC[COC Films], Kunststoffe 87 (1997) 1, pp. 58-62) with a glass transitiontemperature Tg of about 160° C. were also fed to the extruder for thebase layer B. The proportional amount of the cycloolefin copolymer (COC)in the entire film was 10% by weight. 1.0% by weight of the UVstabilizer 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-hexyloxyphenol(®Tinuvin 1577 from Ciba-Geigy, Basle, Switzerland) and 4% by weight ofphosphorus-containing flame retardant were also added.

[0159] Tinuvin 1577 has a melting point of 149° C. and is thermallystable up to about 330 C. The UV stabilizer Tinuvin 1577 is fed in theform of a masterbatch. The masterbatch is composed of 5% by weight ofTinuvin 1577 as active component and 95% by weight of PET with astandard viscosity of SV (DCA) 810, corresponding to an intrinsicviscosity IV (DCA) of 0.658 dl/g.

[0160] The flame retardant is the organic phosphorus compound dimethylmethylphosphonate, ®Amgard P 1045 from Albright & Wilson, which issoluble in PET.

[0161] The flame retardant is also fed in the form of a masterbatch. Themasterbatch is composed of 20% by weight of flame retardant and 80% byweight of PET with a standard viscosity SV (DCA) of 810.

[0162] The two masterbatches had bulk densities of 750 kg/m3. Extrusionfollowed by stepwise longitudinal and transverse orientation was used toproduce a white, opaque, single-layer film with an overall thickness of23 μm.

[0163] Base layer B was a mixture of: 85.0% by weight of polyethyleneterephthalate homopolymer with an SV of 800 10.0% by weight ofcycloolefin copolymer (COC) from Ticona, Topas 6015  1.0% by weight ofTinuvin 1577  4.0% by weight of Amgard P 1045

[0164] The production conditions in the individual steps of the processwere: Extrusion: Temperatures Base layer: 280° C. Take-off rolltemperature: 30° C. Longitudinal Temperature: 80-125° C. stretching:Longitudinal stretching ratio: 4.2 Transverse Temperature: 80-135° C.stretching: Transverse stretching ratio: 4 Setting: Temperature: 230° C.Duration: 3 s

[0165] The film had the required good properties and the desiredhandling properties, and the desired processing performance. Theproperties achieved in films produced in this way are shown in Table 2.

EXAMPLE 2 (inventive)

[0166] A change was made from Example 1 by adding 50% by weight ofregrind to the base layer. The amount of COC in the film thus producedwas again 10% by weight, the amount of UV stabilizer was 1% by weight,and the amount of flame retardant was 4% by weight. The processparameters were unchanged from Example 1. A visual observation was madeof any yellow coloration of the film. It can be seen from Table 2 thathardly any yellow coloration of the film could be observed.

[0167] Base layer B was a mixture of: 42.5% by weight of polyethyleneterephthalate homopolymer with an SV of 800 50.0% by weight of regrind(90% by weight of polyester + 10% by weight of Topas 6015 + 1% by weightof Tinuvin 1577)  5.0% by weight of cycloolefin copolymer (COC) fromTicona, Topas 6015  0.5% by weight of Tinuvin 1577  2.0% by weight ofAmgard P 1045

EXAMPLE 3 (inventive)

[0168] Example 1 was now modified by producing a film of thickness 96μm. The amount of COC in the film was 8% by weight, the amount ofTinuvin 1577 was 1% by weight, and the amount of flame retardant was 4%by weight. The process parameters were unchanged from Example 1. Avisual observation was made of any yellow coloration of the film. It canbe seen from Table 2 that no yellow coloration of the film was observed.

[0169] Base layer B was a mixture of: 87.0% by weight of polyethyleneterephthalate homopolymer with an SV of 800  8.0% by weight ofcycloolefin copolymer (COC) from Ticona, Topas 6015  1.0% by weight ofTinuvin 1577  4.0% by weight of Amgard P 1045

EXAMPLE 4 (inventive)

[0170] A change was made from Example 3 by adding 50% by weight ofregrind to the base. The amount of COC in the film was again 8% byweight, the amount of Tinuvin 1577 was 1% by weight, and the amount offlame retardant was 4% by weight. The process parameters were unchangedfrom Example 1. A visual observation was made of any yellow colorationof the film. It can be seen from Table 2 that hardly any yellowcoloration of the film could be observed.

[0171] Base layer B was a mixture of: 43.5% by weight of polyethyleneterephthalate homopolymer with an SV of 800 50.0% by weight ofself-generated regrind (90% by weight of polyester + 10% by weight ofTopas 6015 + 1% by weight of Tinuvin 1577)  4.0% by weight ofcycloolefin copolymer (COC) from Ticona, Topas 6015  0.5% by weight ofTinuvin 1577  2.0% by weight of Amgard p 1045

COMPARATIVE EXAMPLE 1

[0172] Example 1 from DE-A 2 353 347 was repeated. The example wasmodified with concomitant use of 50% by weight of regrind. It can beseen from Table 2 that marked yellow coloration of the film wasobserved. In addition, the roughness of the film is much too high formany applications, and the gloss is too low for many applications. It ishighly probable that this is attributable to the use of other polymericadditives.

[0173] Base layer B was a mixture of: 47.5% by weight of polyethyleneterephthalate homopolymer with an SV of 800 50.0% by weight ofself-generated regrind (95% by weight of polyester + 5% by weight ofpolypropylene)  2.5% by weight of polypropylene

COMPARATIVE EXAMPLE 2

[0174] Example 1 from EP-A 0 300 060 was repeated. The example wasmodified with concomitant use of 50% by weight of regrind. It can beseen from Table 2 that marked yellow coloration of the film wasobserved. In addition, the roughness of the film is much too high formany applications, and the gloss is too low for many applications. It ishighly probable that this is attributable to the use of other polymericadditives.

[0175] Base layer B was a mixture of: 45.0% by weight of polyethyleneterephthalate homopolymer with an SV of 800 50.0% by weight ofself-generated regrind (95% by weight of polyester + 5% by weight ofpolypropylene)  5.0% by weight of polypropylene

COMPARATIVE EXAMPLE 3

[0176] Example 1 from EP-A 0 360 201 was repeated. The example wasmodified with concomitant use of 50% by weight of regrind. It can beseen from Table 2 that marked yellow coloration of the film wasobserved. In addition, the roughness of the film is much too high formany applications, and the gloss is too low for many applications. It ishighly probable that this is attributable to the use of other polymericadditives.

[0177] Base layer B was a mixture of: 40.0% by weight of polyethyleneterephthalate homopolymer with an SV of 800 50.0% by weight ofself-generated regrind (95% by weight of polyester + 5% by weight ofpolypropylene) 10.0% by weight of polypropylene

COMPARATIVE EXAMPLE 4

[0178] Example 1 from DE-A 195 40 277 was repeated. The example wasmodified with concomitant use of 50% by weight of regrind. It can beseen from Table 2 that marked yellow coloration of the film wasobserved. In addition, the roughness of the film is much too high formany applications, and the gloss is too low for many applications. It ishighly probable that this is attributable to the use of other polymericadditives.

[0179] Base layer B was a mixture of: 43.5% by weight of polyethyleneterephthalate homopolymer with an SV of 800 50.0% by weight ofself-generated regrind (95% by weight of polyester + 5% by weight ofpolystyrene)  6.5% by weight of polystyrene

[0180] Each of the films produced in Examples 1 to 4 and ComparativeExamples 1 to 4 was exposed to 1000 hours per side of weathering with anAtlas Ci65 Weather-Ometer. The films produced in the inventive Examples1 to 4 showed no significant changes in properties.

[0181] In contrast, the films of Comparative Examples 1 to 4 showedsurface cracks and embrittlement phenomena after 1000 hours ofweathering with an Atlas Ci65 Weather-Ometer. It was thereforeimpossible to measure any accurate property profile for these films, inparticular their mechanical properties. In addition, the films showedmarked visible yellow coloration.

[0182] Each of the films produced in Examples 1 to 4 and ComparativeExamples 1 to 4 was treated at a temperature of 100° C. for 200 hours ina circulating-air drying cabinet. The mechanical properties of the filmsof Examples 1 to 4 are unchanged. The films show not even the slightestsign of embrittlement phenomena, whereas the films of the comparativeexamples have cracks visible to the naked eye and attempts to fold themlead to fracture.

[0183] The films of Examples I to 4 comply with the requirements forconstruction material classes B 2 and B I to DIN 4102 Part 2/Part 1, andthey pass the UL 94 test, but this is not true for the films ofComparative Examples 1 to 4.

What is claimed is:
 1. A white, biaxially oriented, flame-retardant andUV-resistant polyester film comprising at least one layer, wherein atleast this layer comprises, based on the weight of this layer, from 2 to60% by weight of a cycloolefin copolymer (COC), where the glasstransition temperature of the COC is within the range from 70 to 270°C., and wherein the layer comprises at least one UV stabilizer as lightstabilizer and a flame retardant, where the flame retardant is feddirectly as a masterbatch to the polyester during film production. 2.The polyester film as claimed in claim 1 wherein the UV stabilizer isfed directly as a masterbatch to the polyester during film production.3. The polyester film as claimed in claim 1 , wherein the COC comprisespolynorbornene, polydimethyloctahydronaphthalene, polycyclopentene orpoly(5-methyl)norbornene.
 4. The polyester film as claimed in claim 1 ,wherein the COC has a glass transition temperature within the range from90 to 250° C., wherein the amount of UV stabilizer is within the rangefrom 0.01 to 5.0% by weight, based on the total weight of the layer, andwherein the amount of flame retardant is within the range from 0.5 to30% by weight, preferably from 1 to 20% by weight, based on the weightof the layer.
 5. The polyester film as claimed in claim 1 , wherein thecycloolefin copolymer (COC) has a glass transition temperature withinthe range from 110 to 220° C., and wherein the UV stabilizer has beenselected from 2-hydroxybenzotriazoles or from triazines or from2-hydroxybenzotriazoles and triazines.
 6. The polyester film as claimedin claim 1 , wherein the whiteness of the film is above 70%, and whereinthe UV stabilizer is2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-hexyloxyphenol or2,2′-methylenebis(6-(2H-benzotriazol-2-yl)-4-(1,1,2,2-tetramethylpropyl)phenol)or 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-hexyloxyphenol or2,2′-methylenebis(6-(2H-benzotriazol-2-yl)-4-(1,1,2,2-tetramethylpropyl)phenol).
 7. The polyester film as claimed inclaim 1 , wherein the opacity of the film is above 55%, and wherein thefilm comprises organic phosphorus compounds as flame retardants.
 8. Thepolyester film as claimed in claim 7 , wherein the organic phosphoruscompounds are soluble in polyethylene terephthalate.
 9. The polyesterfilm as claimed in claim 1 , wherein the gloss of the film is above 80,and wherein the film comprises, as flame retardant, the bisglycol esterof 2-carboxyethyl(methyl)phosphinic acid or of the cyclic anhydridethereof, 2-methyl-2,5-dioxo-1,2-oxophospholane.
 10. The polyester filmas claimed in claim 1 , wherein the layer comprises from 0.5 to 25% byweight of other vacuole-inducing fillers or white fillers or pigment orvacuole-inducing fillers and white fillers or vacuole-inducing fillersand pigment, in each case based on the weight of the layer.
 11. Thepolyester film as claimed in claim 1 , wherein at least one outer layerhas been arranged on the COC-containing layer, and wherein the UVstabilizer and the flame retardant are present in the outer layer(s).12. The polyester film as claimed in claim 11 , wherein an intermediatelayer has been arranged between the COC-containing layer and the outerlayer.
 13. The polyester film as claimed in claim 1 , wherein the filmhas one layer and is composed of the COC-containing layer.
 14. A white,biaxially oriented, flame-retardant, UV-resistant polyester filmcomprising at least one layer, which comprises, based on the weight ofthis layer, from 2 to 60% by weight of COC, where the opacity of thefilm is above 60%, wherein the film also comprises from 0.1 to 5% byweight, of a UV stabilizer as light stabilizer, and also comprises anamount within the range from 1 to 20% by weight of a flame retardant,based in each case on the weight of the layer comprising the UVstabilizer or comprising the flame retardant or comprising the UVstabilizer and the flame retardant.
 15. The white, biaxially oriented,flame-retardant, UV-resistant polyester film comprising at least onelayer, which comprises, based on the weight of this layer, from 2 to 60%by weight of COC, and the whiteness of which is above 70%, wherein thefilm also comprises from 0.1 to 5% by weight, of a UV stabilizer aslight stabilizer, and also comprises an amount within the range from 1to 20% by weight of a flame retardant, based in each case on the weightof the layer comprising the UV stabilizer or comprising the flameretardant or comprising the UV stabilizer and the flame retardant. 16.The white, biaxially oriented, flame-retardant, UV-resistant polyesterfilm comprising at least one layer, which comprises, based on the weightof this layer, from 2 to 60% by weight of COC, and the gloss of which isabove 80, wherein the film also comprises from 0.1 to 5%, of a UVstabilizer as light stabilizer, and also comprises an amount within therange from 1 to 20% by weight of a flame retardant, based in each caseon the weight of the layer comprising the UV stabilizer or comprisingthe flame retardant or comprising the UV stabilizer and the flameretardant.